1. Field of the Invention
The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to an apparatus that connects perforating guns. Yet more specifically, the present invention relates to a perforating gun connector utilizing corresponding tapered ends to facilitate connections thereof. Yet even more specifically, the present invention relates to an automated method of connecting perforating guns with a perforating gun connector.
2. Description of Related Art
Perforating guns are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore, and the casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.
Included with the perforating guns are shaped charges that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge at very high velocity in a pattern called a “jet”. The jet penetrates the casing, the cement and a quantity of the formation.
Often more than one perforating gun is required to perforate a wellbore. In these instances multiple perforating guns are inserted into a wellbore and connected end to end with a perforating gun connector. Generally the perforating gun connectors are made from two sections, where one section is secured to one perforating gun, the other section secured to another perforating gun, and the two connector sections are then joined. Thus each section has two ends, where one end is formed for connection to a perforating gun, and the other end is formed for connection to the other section.
Within each connector is a length of detonating cord that transmits a detonation wave that is ultimately transferred to the shaped charges. Since the perforating gun connection is made up of two separate sections, a first booster charge is disposed in one of the sections and a second booster charge is disposed in the adjacent section. Thus the detonation energy is transferred from one section to its adjacent section by when the first booster charge detonates it transfers an explosive shock wave across the air gap thereby igniting the second booster charge. Ignition of the second booster charge in turn transfers the detonation wave to its attached detonation cord.
Generally, both ends of the sections are threaded for connecting to the perforating gun and to the other section, thus connection to the perforating gun and to the other section is accomplished by screwing the section onto the perforating gun and other section. Typically, after the sections of the connectors are attached to the perforating guns, the perforating gun of one of the sections is inserted into the wellbore and secured such that the section is pointing up out of the wellbore. The other section, with its attached perforating gun, is hoisted above the secured section and positioned so that the hoisted section is coaxial with the secured section. The hoisted section is then lowered onto the secured section and the hoisted perforating gun and hoisted section are axially rotated in order to screw the hoisted section onto the secured section.
One of the problems with this technique is that current connection devices require a manual attendant to be present at the site where the perforating gun connector sections are being joined. Attendants are required to guide the hoisted section cleanly into the secured section to ensure the sections are substantially coaxially aligned and to prevent cross threading. Further, in situations where the first and second booster charges within the connectors are exposed, attendants are needed to prevent the sections from impacting one another in a manner that could prematurely detonate the explosives within the connectors. Also, these attendants must inspect the sections of the connectors to check that the first and second booster charges are properly in place before being inserted into the wellbore.
This currently known operation of connecting perforating guns however is hazardous to attendant personnel who actually perform the connecting. Because of the mass of the perforating guns and their respective connectors, the attendant personnel must remain vigilant to avoid becoming pinned between the hoisted section and the secured section. Further, the presence of the high explosives within the connectors and the perforating guns require extra care. While these handling considerations could be greatly reduced if the connection procedure were automated, all other known connection means on the perforating gun connection sections are incapable of being reliably connected by mechanical means, such as with a pipe-handling device. For example, prior art perforating gun connectors that are coupled with a pipe-handling device are prone to become cross-threaded. Further the controllability of mechanical coupling devices make it difficult to accurately insert a hoisted section into a secured section, which can not only lead to the cross threading problem, but can also result in possible damage to the explosives within the connectors.
Therefore, there exists a need for an apparatus and a method to connect perforating guns that increases the reliability of connecting perforating guns, substantially reduces the handling problems associated with coupling perforating guns, and provides for an automated method of reliably connecting perforating guns.